Generally speaking, the present invention concerns the field of sensors of all types of force (force, pressure, moment or angular or linear acceleration) using resistive gauges disposed in two Wheatstone bridges oriented in two different directions.
This type of force sensor can be integrated into any system in which it is required to measure a force (pneumatic, joystick for video games, etc.) or an acceleration (air bag triggering in an automobile, pacemaker, etc.).
A prior art force sensor is described in particular in the document U.S. Pat. No. 4,745,812.
That sensor produced by microtechnology techniques includes piezoresistive detection elements disposed in a double Wheatstone bridge in a plane of a deformable support. These gauges are arranged in two perpendicular directions to detect the components in space of the force applied to the deformable support.
The imbalance of a first Wheatstone bridge, obtained by interconnecting four gauges aligned in a first direction, is proportional to the component of the force in that first direction. The imbalance of a second Wheatstone bridge, obtained by interconnecting four gauges aligned in a second direction, is proportional to the component of the force in that second direction. The common mode of the two bridges is proportional to the component of the applied force in a direction perpendicular to the plane of the deformable support.
During the production of the structure of such a sensor by microtechnology means, the interconnection of the Wheatstone bridges necessitates producing insulated crossovers of the conductive tracks. In practice, these insulative crossovers are obtained by stacking two metallic levels. Such stacking represents a fabrication overcost and risks of failure of the sensor with reduced efficiency.